Fig. 3

Mupirocin resistance affects the relative fitness of S. aureus. a The effect of mup^R on the relative fitness of S. aureus was determined in strains with and without a functioning Agr system by direct competition in TSB. There was no difference in fitness in the Agr+ background, but in the absence of Agr, the mup^R strain was less fit. Control competition of an Agr+ vs an Agr− strain is shown. b The effect of mupR on relative fitness was determined by individual culture in a nutrient-poor environment (0.1× TSB) supplemented with 5% horse blood. At the early stages of growth (0–6 h) the mup^S strain was more fit than both the Agr− and mup^R strains. Whereas between 6 and 24 h when the nutrients in the TSB were depleted and cell lysis became necessary, the mup^S strains were relatively more fit than both the Agr− and mup^R strains. c After 24 h of growth in the 0.1× TSB + 5% horse blood medium the Agr+ strain releases more haem into the supernatant relative to the Agr− and mup^R strains